package vn.com.vhc.library;

import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

public class SimpleCrypto {
	public String encrypt(String seed, String cleartext) throws Exception {
        byte[] rawKey = getRawKey(seed.getBytes());
        byte[] result = encrypt(rawKey, cleartext.getBytes());
        return toHex(result);
		}
		
		public String decrypt(String seed, String encrypted) throws Exception {
		        byte[] rawKey = getRawKey(seed.getBytes());
		        byte[] enc = toByte(encrypted);
		        byte[] result = decrypt(rawKey, enc);
		        return new String(result);
		}
		
		private byte[] getRawKey(byte[] seed) throws Exception {
		        KeyGenerator kgen = KeyGenerator.getInstance("AES");
		        SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
		        sr.setSeed(seed);
		    kgen.init(128, sr); // 192 and 256 bits may not be available
		    SecretKey skey = kgen.generateKey();
		    byte[] raw = skey.getEncoded();
		    return raw;
		}
		
		
		private byte[] encrypt(byte[] raw, byte[] clear) throws Exception {
		    SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
		        Cipher cipher = Cipher.getInstance("AES");
		    cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
		    byte[] encrypted = cipher.doFinal(clear);
		        return encrypted;
		}
		
		private byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception {
		    SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
		        Cipher cipher = Cipher.getInstance("AES");
		    cipher.init(Cipher.DECRYPT_MODE, skeySpec);
		    byte[] decrypted = cipher.doFinal(encrypted);
		        return decrypted;
		}
		
		public String toHex(String txt) {
		        return toHex(txt.getBytes());
		}
		public String fromHex(String hex) {
		        return new String(toByte(hex));
		}
		
		public byte[] toByte(String hexString) {
		        int len = hexString.length()/2;
		        byte[] result = new byte[len];
		        for (int i = 0; i < len; i++)
		                result[i] = Integer.valueOf(hexString.substring(2*i, 2*i+2), 16).byteValue();
		        return result;
		}
		
		public String toHex(byte[] buf) {
		        if (buf == null)
		                return "";
		        StringBuffer result = new StringBuffer(2*buf.length);
		        for (int i = 0; i < buf.length; i++) {
		                appendHex(result, buf[i]);
		        }
		        return result.toString();
		}
		private final static String HEX = "0123456789ABCDEF";
		private void appendHex(StringBuffer sb, byte b) {
		        sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f));
		}

}
